A reference signal source in a several MHz frequency band used for electronic devices such as a portable device, an information communication device, and a measuring device includes: an AT cut quartz crystal resonator; a DT cut quartz crystal resonator (a contour shear mode quartz crystal resonator); and a contour resonator such as a Lame mode quartz crystal resonator and a quasi Lame mode quartz crystal resonator.
Conventionally, as a frequency adjustment for a contour resonator, a method to adjust a resonance frequency by sputtering a metal film of a vibrating portion using atomic particles and/or molecular particles, or ion particles, and a method to adjust a resonance frequency by attaching a metal film to the vibrating portion have been employed (e.g. refer to Patent Citation 1).
Further, Non Patent Citation 1 shows that in a Lame mode quartz crystal resonator indicated by YX1t phi/theta of IRE (abbreviation of Institute of Radio Engineers, that is, current IEEE) standard, a resonance frequency (contour vibration frequency) f of an individual quartz substrate is derived by a frequency equation shown in Math (9) in the citation. In addition, by this frequency equation, a resonance frequency of an individual excitation electrode can also be derived. This is also shown in Non Patent Citation 2.    Patent Citation 1: Japanese Unexamined Patent Publication No. 2005-94733 (page 23, FIG. 5)    Non Patent Citation 1: “Lame-mode quartz-crystal resonator formed by an etching method” by Hirofumi Kawashima, and Masaru Matsuyama in the 24th EM symposium, page 11 to 16, Math (2), conditional clause and Math (9)    Non Patent Citation 2: “Development of a small-sized Lame-mode quartz-crystal resonator” by Katsuya Mizumoto, Masashi Akino, Tsuyoshi Nishizuka, Hideki Ashizawa, Masahide Marumo, and Masato Amemiya in the 35th EM symposium, page 31 to 34